1. Field of the Invention
The present invention relates generally to image processing apparatuses, and more specifically, to an image processing apparatus such as a copying machine and a printer which converts read data into data in reproduced color and forms a multi-color image.
2. Description of the Related Art
In printers which reproduce images in full color, digital image data R, G, and B corresponding to red, green, and blue (primary colors) read from an original is converted into data of three colors for color reproduction, cyan (C), magenta (M) and yellow (Y) (complementary colors) for reproduction of the image.
Therefore, a data processing apparatus for converting digital data in three colors, red, green and blue obtained by scanning an original into three reproduction color data for image reproduction is required.
Black obtained by mixing cyan, magenta, and yellow cannot be reproduced sharp enough by the effect of the spectral characteristic of each toner. Therefore, subtractive color mixing process with reproduction color data Y, M and C and addition of black with black data K are employed to improve the reproducibility of black. In addition, a masking correction with a masking coefficient is conducted in order to compensate for deviation from ideal filter and toner characteristics in reading colors.
It is however difficult to reproduce colors at a low difference in color in the entire range of the color space using a masking coefficient fixed to one kind. A method of dividing the color space into a number of regions and using different masking coefficients for the regions has been suggested. Although color reproducibility is increased by the method, sharp change in masking coefficient at a boundary of colors in the color space can result in harshness or a pseudo-contour.
Thus, a color image processing apparatus has been suggested which has a plurality of matrixes for color correction, conducts color correction of color component signals in parallel using the matrixes, and combines the outputs in a prescribed ratio.
Such a conventional image processing apparatus requires a plurality of circuits for color correction, and therefore the circuit configuration will be complicated. The number of matrixes for color correction corresponding to the color correction circuits is fixed to the number of prescribed color regions, and change in the number of color regions cannot be coped with, and therefore, such an apparatus would not be suitable.
Meanwhile, another image processing apparatus having a color change function has been suggested which identifies a specified color from read data of R, G, and B as input parameters using a table index and changes the color. If such identification of a specified color is made in a binary manner (as whether it belongs to the color or not), however, portions to be converted are discretely generated for colors belonging to boundary portions on the color space and may result in harshness. The pseudo-contour is also inevitably produced.